In my U.S. Pat. No. 4,691,951, I have described a door set of a type having a pair of doorknobs which are coupled together by a pair of diametrically opposite rods which are eccentric to the axis of rotation of the doorknobs. A hook of the door bolt engages one of these rods, the door bolt being biased outwardly by a coil spring in a housing, casing or sleeve which is affixed in the edge of the door so that the bolt can emerge to engage a stroke on the door jamb. When one of the doorknobs is rotated, the bolt is retracted allowing the door to open.
To permit adjustment, the bolt is formed in two parts which are connected by a screw coupling, namely a stud formed with an external thread which is provided with the hook and the engagement portion of the bolt which is internally threaded to threadedly engage this stud.
A similar structure is illustrated in German Utility Model DE-GM No. 85 29 711.
It will be apparent from the aforementioned patent and Utility Model, that the hook on the single arm of the stud, in engagement with the eccentric rod, creates a preferred opening direction for the knob rotation, i.e. when either knob is rotated in the sense that the engaged rod retracts the bolt, the bolt will be withdrawn from the strike in an appropriate manner.
However, rotation in the opposite sense may pose a problem since the rod may leave the hook in the case where the hook is open. Of course it is possible in that situation to provide the knob so that it cannot rotate in the undesired sense, but this poses a constraint on the door set which may be undesirable.
It is, therefore, frequently advantageous to provide the door set so that the bolt can be retracted in the bolt housing in either sense of rotation of either knob. This presents a simplification of operation and allows the door set to be better utilized by the elderly, the disabled or in emergency situations as is required by law in many countries.